This invention relates to electrical rotating machines and more particularly to electric motors of the type in which the rotor of the motor turns in discreet increments or steps, and to a method for making such motors. The invention more specifically relates to a stepper motor utilizing a rotor preferably having a diameter that is at least 60% of the motor diameter to provide substantially more torque than equivalent-sized conventional motors.
The use of multiple field coils with a single non-salient pole rotor in a stepper motor is well-known in the art and is shown by such prior patents as U.S. Pat. Nos. 4,241,270 and 4,274,026. To prevent radial displacement of the stator within the motor assembly, stator pole pieces have heretofore been notched such that adjacent stator pole pieces may be frictionally interlocked. Representative motors of this type are disclosed, for example, in U.S. Pat. Nos. 4,333,026 and 3,495,113. These prior art references, however, do not provide for any number of individual stator phase assemblies including a plurality of stator pole pieces and a notched field ring to be interlocked together. Thus, it would be advantageous if one could link more than two stator assemblies, with each assembly being of different phase such that the motor could operate in more than two phases. In addition, it is desirable to provide a stepper motor assembly wherein the same parts can be used to achieve more than two phases, and hence, reduce tooling costs.
The stepper motor of the present invention also includes, in a preferred embodiment, a rotor having a diameter that is at least approximately 55% of the motor diameter and thus produces substantially more torque than equivalent sized conventional motors.
The present invention is directed towards solving these problems and provides a workable and economical solution to them.